The present invention concerns an electronic device, or dimmer, for regulating the power supply. Specifically, said dimmer makes possible, in a simple, reliable, effective, and acoustically noiseless way, to supply loads, in particular lighting power devices, such as filament lamps, for motion picture, television, and theatre applications.
The present invention further concerns a system for controlling and regulating the power supply applied to a plurality of loads, comprising such dimmers.
A dimmer is an electronic device capable to control alternate voltage applied to a load, generally a filament lamp, through delivering a selected portion of the mains sinusoid by means of an electronic power switch. In particular, when the power supply is decoupled from the load at the beginning of each half-cycle of the mains sinusoid, the dimmer applies to the load a waveform named forward phase control or FPC, having very steep power up fronts and sinusoidal power down. Conversely, when the power supply is coupled to the load at the beginning of each half-cycle of the mains sinusoid, the dimmer applies to the load a waveform named reverse phase control or RPC, having sinusoidal power up and very steep power down fronts.
After the development of the first power solid state electronic devices, which assure a controlling capability better than valves, dimmers have been developed employing devices know as triacs, or bidirectional thyristors, operating as electronic switches; such triacs comprise two controlled rectifiers, or SCR, connected in antiparallel configuration. A triac may be turned on in any moment, and it turns off only when the current becomes smaller than a minimum conduction value.
Due to such characteristics, said dimmers operate according to the FPC control. Since very steep leading edges are harmful for the lamp filaments, besides producing both electrical and acoustic noise, in order to slow the leading edges down, said dimmers are provided with large inductors, which assure high efficiency and great circuit simplicity.
However, such dimmers have the drawback to be very expensive and still very noisy.
In recent years, dimmers have been developed employing as electronic switches, power solid state devices known as insulated gate bipolar transistors, or IGBTs. With respect to triacs, IGBTs offer the advantage to be able to be controlled for turning on and off, and to be able to operate also in linear region and to be progressively turned off.
In particular, U.S. Pat. No. 5,004,969 discloses a phase control power switching circuit having a couple of IGBTs, connected in reverse series configuration between a load and alternate current source, for controlling the current flow through the load. The two IGBTs are alternatively driven through commutating means such a way that each IGBT alternatively operates between conduction and interdiction at the desired phase angle of the current flow. In particular, such a circuit, which is usable as a dimmer, is based on the interaction of a constant frequency source, a flip-flop, and a delay circuit.
However, the dimmer disclosed in U.S. Pat. No. 5,004,969, which is described as operating according to the RPC control, has some drawbacks.
First of all, it is not capable to regulate the descent slope of the power down fronts of the RPC waveform applied to the load (similarly, it would not be capable to regulate the rise slope of the power up fronts of FPC waveform). This produces quicker power down times for lower values of current delivered to the load, and, hence, it makes complex to select the desired phase angle in order to control the power up times of the load lamps.
Moreover, efficiency is smaller, the dimmer suffers from a high circuit complexity and is acoustically rather noisy.
U.S. Pat. No. 5,239,255 discloses a phase controlled power modulation system which again employs a couple of IGBTs, connected in reverse series configuration between a load and an alternate current source, for modulating the power supply applied to the load. The two IGBTs are driven by a transition shaper that controls the rate of change of the voltage applied to the load. The dimmer further comprises a phase controller, for controlling the transition shaper, a device for protecting the IGBTs, and an asymmetric waveform selector. The dimmer may operate according to the FPC control, according to the RPC control, or, by means of the asymmetric waveform selector, according to an asymmetric hybrid control, wherein the power delivered to the load during the first half-cycle of the supply alternate current is different from the power delivered during the second half-cycle.
However, also the dimmer disclosed in U.S. Pat. No. 5,239,255 has some drawbacks.
First of all, in case overload conditions occur, due for example to a situation of cold lamp, the filament of which has a resistance about ten times lower than the one of the filament at operative temperature, transition shaper voltage control does not detect conditions of excessive current delivered to the load. Therefore, monitoring of possible overload conditions is carried out by the protecting device which indirectly operates on the shaper through the asymmetric waveform selector, making the dimmer circuit extremely complex. Moreover, despite of such circuit complexity, the dimmer is not much versatile, since the slope of both power up and power down fronts may be selected among very few values predetermined by the circuit components.
Consequently, the dimmer is also expensive and not completely effective.
Furthermore, it is still acoustically noisy under overload conditions.
Other dimmers, which are presently available on the market, comprise an IGBT and a rectifier bridge, or two IGBTs with reverse conducting diode. Such dimmers have RPC operating characteristics, wherein the descent time of the power down front is limited by IGBT dissipation. Time of about 500 microseconds may be obtained under reasonable dissipation. Also, such dimmers may similarly operate according to FPC operating mode.
Even offering some advantages, such as sinusoidal leading edges having reduced noise and trailing edges having variable slope obtained without using expensive large inductors, these last dimmers still have the drawbacks of having a low efficiency and a considerable circuit complexity, and of being excessively noisy for applications to show environments.
Acoustic and electrical noise of presently available dimmers forces to place all dimmers far away from the supplied lamps which are used in show environments, preferably within a dedicated room which is far and acoustically insulated from the show room where the lighting devices supplied by the same dimmers are mounted. This causes the presence of a lot of cables in the room to be lighted in all the cases where a multiplicity of lamps is needed, as it happens in television or motion picture studios, or in theatre stages, producing high cost of the electric installation. Moreover, currents with high harmonic content pass through the cables, causing cross talks and interference among the various circuits.
It is therefore an object of the present invention to provide an electronic device, or dimmer, for regulating the power supply applied to a load, which is both acoustically and electrically noiseless during supplying operations of power loads, in particular lighting power devices.
It is still object of the present invention to provide such an electronic device which make possible, in a reliable and effective way, to regulate the rise slope of the power up fronts and the descent slope of the power down fronts of the power waveforms applied to the load.
It is another object of the present invention to provide such a device which has a high efficiency and a great circuit simplicity, consequently being simple to be realised and having cost at least comparable to the cost of conventional dimmers.
It is specific subject matter of this invention an electronic device, or dimmer, for regulating the power supply applied to a load, the device comprising an insulated gate bipolar transistor or IGBT, the IGBT having a first operating mode in which it is off and does not allow any current to pass, a second operating mode in which it is on and the current passing therein is substantially limited by characteristics of an external circuit connected to it, and a third linear region operating mode, in which the current passing therein is limited by a value proportional to the gate voltage, the IGBT being connected to a rectifier bridge, apt to be connected to a load and to a mains connected in series to each other, the device further comprising a processing and controlling unit, the device being characterised in that said processing and controlling unit includes digital processing means and in that the device comprises ramp generating means driven by said processing and controlling unit, apt to generate a ramp voltage signal at an output terminal connected to the IGBT gate, so as to drive the IGBT in linear region.
It is obvious to provide that other embodiments of the device according to the invention have a processing and controlling unit driving more ramp generating means, each one of which drives in turn one or more IGBT, each connected to a corresponding load through a rectifier bridge.
Preferably according to the invention, said ramp generating means comprises a Digital to Analogue (or D/A) converter, driven by said digital processing means, the D/A converter having an output connected to the not inverting input of a differential amplifier, the inverting input of which is connected to an amperometric transformer, in turn connected in series to the IGBT, the inverting input of the differential amplifier receiving from the amperometric transformer a voltage signal proportional to the current passing into the IGBT, an output of the differential amplifier being connected to the IGBT gate.
Always according to the invention, said ramp generating means may comprise one or more stages for amplifying and/or stabilising the signal generated at said output of the D/A converter.
Still according to the invention, said processing and controlling unit may be connected to the amperometric transformer in such a way to receive a voltage signal proportional to the current passing into the IGBT.
Further according to the invention, the device may include power up means and power down means, controlled by said processing and controlling unit, connected to the IGBT gate and apt to turn on and off, respectively, the IGBT.
Preferably according to the invention, said power up means includes a p-n-p transistor and said power down means includes a n-p-n transistor.
Always according to the invention, the device may comprise IGBT protection switching means, connected between the IGBT gate and a circuit ground, apt to take on an open configuration, in which the IGBT gate is apt to be driven by said ramp generating means, or a closed configuration, in which the IGBT gate is connected to circuit ground.
Still according to the invention, the configuration taken by said switching means may be controlled by said processing and controlling unit.
Further according to the invention, the configuration taken by said switching means may be controlled by an output of a comparator including a first input, connected to the amperometric transformer so as to receive a voltage signal proportional to the current passing into the IGBT, and a second input, at which a first threshold voltage value, preferably adjustable, is present.
Always according to the invention, said processing and controlling unit may be connected to first detecting means in such a way to receive a voltage signal related to the configuration taken by said switching means.
Preferably according to the invention, said switching means comprises a thyristor or SCR (Silicon Controlled Rectifier), the anode of which is connected to the IGBT gate.
Still according to the invention, the device may further comprise temperature sensor means, apt to detect the IGBT temperature, which is connected to said processing and controlling unit.
Further according to the invention, said processing and controlling unit may be apt to drive said ramp generating means in such a way that:
when the detected IGBT temperature is lower than a first temperature threshold value T1, the duration of the ramp voltage signal is equal to a first interval D1,
when the detected IGBT temperature is higher than the first temperature threshold value T1, the duration of the ramp voltage signal is equal to a second interval D2, where D2 less than D1.
Preferably according to the invention, D1 ranges from 450 to 550 microseconds and D2 ranges from 150 and 250 microseconds.
Always according to the invention, said processing and controlling unit may be apt to drive said power down means in such a way that:
when the detected IGBT temperature is higher than a second temperature threshold value T2, where T2 greater than T1, the IGBT is kept in off condition until the detected IGBT temperature is lower than a third temperature threshold value T3, where T3 less than T2, preferably with T3 less than T1.
Still according to the invention, said processing and controlling unit may be connected to second detecting means in such a way to receive a voltage signal proportional to the voltage at the IGBT collector terminal.
Further according to the invention, the device may also comprise power supplying means connected to the mains and to said processing and controlling unit, so as to deliver to said processing and controlling unit at least one signal of synchronism with a supply periodic signal of the mains.
Always according to the invention, said supply periodic signal may be a sinusoidal signal and the device may be apt to apply to the load a reverse phase control, or RPC, waveform and/or a forward phase control, or FPC, waveform.
Moreover, thanks to the ramp generating means, to the power up means and to the power down means, the device according to the invention may drive the IGBT in such a way to apply to the load any power supply waveform.
Preferably according to the invention, said digital processing means includes a first microprocessor.
Still according to the invention, said digital processing means may be connected to a first communication interface unit in conformity with the DMX protocol.
Further according to the invention, said digital processing means may also be connected to a second communication interface unit in conformity with the CAN protocol.
Preferably according to the invention, said digital processing means includes a second microprocessor, intercommunicating with the first microprocessor and connected to the first communication interface unit and to the second communication interface unit.
It is further specific subject matter of this invention a system for controlling and regulating the power supply applied to a plurality of loads, each one of which is connected in series to a mains, the system comprising one electronic device, or dimmer, for each load of said plurality, for regulating the power supply applied to a load, the system further comprising a control central station connected to each one of said dimmers, for controlling the operation thereof, the system being characterised in that each dimmer is an electronic device for regulating the power supply applied to a load as previously described, which is mounted onto a supporting element of the corresponding load, and in that the system comprises a sole power supply cable, having a shunt for each one of the loads of said plurality.
Always according to the invention, the control central station may be apt to monitor the operation of each one of the dimmers regulating and controlling loads of said plurality.
Preferably according to the invention, said loads are lighting power devices.